In cystic fibrosis several functions of airway epithelia are abnormal, and deficiencies in both Cl.sup.- transport and Na.sup.+ absorption are well documented. See, e.g. Knowles et al., Science 221, 1067 (1983); Knowles et al., J. Clin. Invest. 71, 1410 (1983). Regulation of ion transport might have potential therapeutic benefit in lung diseases characterized by abnormalities in epithelial ion transport, e.g., cystic fibrosis.
One therapeutic goal in cystic fibrosis and other pulmonary diseases in which the water content of the mucous is altered is to hydrate the lung mucous secretions, so that the secretions may be thereafter more easily removed from the lungs by mucociliary action or simple coughing. The use of aerosolized amiloride to hydrate mucous secretions is described in U.S. Pat. No. 4,501,729 to Boucher et al. Amiloride appears to block Na.sup.+ reabsorption by airway epithelial cells, and therefore inhibits water absorption from the mucous. While an important breakthrough in providing treatments for cystic fibrosis, a potential problem with amiloride treatments is the relatively short duration of action of amiloride.
A different therapeutic approach for hydrating lung mucous secretions is exemplified by techniques that involve the administration of ATP or UTP, which appear to stimulate chloride secretion from respiratory epithelial cells. See, e.g., U.S. Pat. No. 5,292,498 to Boucher.
In view of the large numbers of people afflicted with cystic fibrosis, there is an ongoing need for new methods for providing methods of hydrating lung mucous secretions and thereby facilitating lung mucous clearance.